Ultrasonic respiration/convulsion monitoring apparatus and method for its use

Abstract

Apparatus for monitoring respiratory and/or convulsive movements includes a closed loop phase lock system which measures changes in the air path length of continuous wave ultrasound transmitted to and reflected from (the chest/abdomen area of) a subject, and provides an output change signal proportional to changes in air path length caused by respiratory effort of the subject. A window/alarm circuit receives the change signal and triggers an alarm if the change signal remains below a preset lower threshold for a selected time interval, as occurs in apnea. An upper threshold may be set and an alarm triggered if the change signal exceeds the upper threshold for a selected time interval, as occurs in the case of convulsions. The apparatus includes means to provide a signal which follows movement of the subject in an unambiguous manner and which will not trigger an alarm due to extraneous (non-subject) movement. A method of monitoring movement of a subject is provided which includes transmitting continuous wave ultrasound from a source to a subject and receiving the reflected ultrasound. The method includes measuring changes in the air path length of the standing wave and providing an output signal which is proportional to the magnitude of the changes and sounding an alarm when the output signal falls outside a preselected range for a predetermined period of time.

What is claimed is: 
     
       1. Apparatus for non-contact monitoring of movement of a subject comprising: (a) ultrasound source means for generating and transmitting to the abdominal/chest area of a person to be monitored coherent ultrasound whose frequency is controllable by application to said source of a control signal, the transmitted sound wave being reflected from said person to provide a reflected sound wave;   (b) receiver means positioned to receive said reflected sound wave;   (c) phase detector means coupled to said ultrasound source means and to said receiver means and adapted to compare the phase of said reflected sound wave to the phase of said transmitted sound wave and to generate a phase difference signal therefrom;   (d) change detection means coupled to said phase detector means to modify said phase difference signal to generate therefrom a change signal which is proportional to changes in the length of the air path of said transmitted and reflected sound waves between said transmitter means and said receiver means, said change signal thereby exhibiting variations representing the amplitude of respiratory motion when said source means and said receiver means are aimed at the breathing person;   (e) frequency adjusting means coupled to said change detection means to receive said change signal and coupled to said generating means to adjust the frequency of said signal voltage in response to said change signal so as to maintain substantially constant the number of wave lengths of ultrasound in said air path despite changes in the length thereof; and   (f) window/alarm circuit means coupled to said change detector means to receive said change signal for determining whether said variations in said change signal lie within a selected range of values representative of proper respiration for a selected interval of time and for sounding an alarm when said change signal does not lie within said selected range for said selected interval of time.   
     
     
       2. The apparatus of claim 1 wherein said change detection means comprises an integrator circuit to integrate said phase difference signal. 
     
     
       3. The apparatus of claim 2 further including lock-loss circuit means coupled to said integrator circuit and operative to reset said integrator circuit to cause said ultrasound source means to attain a preset center frequency when said integrator circuit approaches its saturation values. 
     
     
       4. The apparatus of claim 1 wherein said frequency adjusting means is coupled between said change detection means and said generating means to define therewith and with said phase detector means a closed loop system operative to adjust the frequency of said signal voltage in response to said change signal so as to maintain substantially constant the number of wave lengths of ultrasonic sound in said air path despite changes in the length thereof. 
     
     
       5. The apparatus of claim 4 wherein said change detection means comprises an integrator circuit to integrate said phase difference sgnal. 
     
     
       6. The apparatus of claim 1 further including means coupled to said change detection means to receive said change signal for providing a visual display of said change signal. 
     
     
       7. Apparatus for monitoring movement of a subject comprising: (a) generating means for generating a signal voltage of ultrasonic frequency;   (b) transmitter means coupled to said generating means to convert said signal voltage for transmission of an ultrasonic sound wave to the abdominal/chest area of a person to be monitored, the transmitted sound wave being reflected from said person to provide a reflected sound wave;   (c) receiver means to receive the reflected sound wave;   (d) phase detector means coupled to said generating means and to said receiver means to receive input therefrom and to generate a difference signal indicative of the phase difference between the transmitted and reflected sound waves;   (e) change detector means comprising an integrator circuit coupled to the output of said phase detector means to receive said difference signal and generate a change signal indicative of transient changes in the phase difference measured by said phase detector means, said change signal being proportional to changes in the length of the air path of said transmitted and reflected sound waves between said transmitter and receiver means, said change signal thereby exhibiting variations representing the amplitude of respiratory motion when said transmitter means and said receiver means are aimed at the breathing person;   (f) frequency adjusting means coupled between said integrator circuit and said generating means to adjust the frequency of said signal voltage in response to said change signal so as to maintain substantially constant the number of wave lengths of ultrasound in said air path despite changes in the length thereof whereby said change signal follows movement of said person in an unambiguous manner; and   (g) window/alarm circuit means coupled to said change detector means to receive said change signal for determining whether said variations in said change signal lie within a selected range of values representative of proper respiration for a selected interval of time and for sounding an alarm when said change signal does not lie within said selected range for said selected interval of time.   
     
     
       8. The apparatus of claim 7 wherein said window/alarm circuit means includes threshold circuit means establising at least one threshold voltage, and means for comparing said change signal to said threshold voltage to determine if said change signal lies within said selected range of values. 
     
     
       9. The apparatus of claim 8 wherein said threshold circuit means establishes an upper threshold voltage and a lower threshold voltage. 
     
     
       10. The apparatus of claim 9 wherein said window/alarm circuit includes first means for generating a window output pulse at the conclusion of events comprising, said change signal crosses said lower threshold voltage with positive slope, does not cross said upper threshold voltage and subsequently recrosses said lower threshold voltage with negative slope, and second means for inhibiting generation of said window output pulse when said change signal crosses said lower threshold with positive slope and then crosses said upper threshold with positive slope, peaks and recrosses said upper threshold with negative slope, then said lower threshold with negative slope. 
     
     
       11. The apparatus of claim 10 further including an analog multiplexer coupled thereto to receive as analog inputs said upper and lower threshold voltages, said change signal and said window output pulses and having its output coupled to a cathode ray oscilloscope to display thereon a simultaneous trace of said analog inputs. 
     
     
       12. The apparatus of claim 7 wherein said transmitter means and said receiver means are supported above the chest/abdomen area of the person to be monitored. 
     
     
       13. The apparatus of claim 7 further including a bandpass filter coupled between said integrator circuit and said window/alarm circuit to bandpass filter said change signal prior to reception thereof by said window/alarm circuit. 
     
     
       14. The apparatus of claim 13 wherein said bandpass filter has a nominal bandwidth of from about 0.1 to 3.4 Hz. 
     
     
       15. The apparatus of claim 13 wherein said integrator circuit includes an operational amplifier having an input resistor connected in series therewith and a feedback capacitor connected in parallel with said operational amplifier between the output of said operational amplifier and the summing junction thereof. 
     
     
       16. The apparatus of claim 15 further including a lock loss circuit means coupled to said integrator circuit and operative to reset said operational amplifier thereof to restore zero initial conditions thereto and to cause said generating means to attain a preset center frequency when said integrator circuit approaches its saturation values. 
     
     
       17. The apparatus of claim 7 wherein said window/alarm circuit includes at least one binary counter adapted to trigger an alarm upon counting a preselected number of pulses, said binary counters being coupled to a monostable multivibrator which resets said binary counter in response to said change signal when said change signal lies within said selected range. 
     
     
       18. The apparatus of claim 7 wherein said transmitter means transmits said ultrasonic sound level at a sound pressure not greater than about 73 db Sound Pressure Level measured at 30 cm from said transmitter means referenced to 0.2 nanobar. 
     
     
       19. A method for monitoring movement of a person comprising: (a) generating a coherent ultrasonic sound wave and transmitting said sound wave to the chest/abdominal area of a person to be monitored for reflection therefrom to provide a reflected ultrasonic sound wave;   (b) receiving said reflected sound wave to define an air path length of the transmitted and reflected untrasonic sound wave;   (c) comparing the phase of said transmitted sound wave to the phase of said received reflected sound wave and determining the difference between the respective measured phases;   (d) measuring changes in the difference between said respective measured phases to provide a change signal which is proportional to changes in said air path length;   (e) adjusting the frequency of the transmitted ultrasonic sound wave in response to said change signal so as to maintain substantially constant the number of wave lengths of ultrasonic sound in said air path length despite changes in the length thereof;   (f) establishing a predetermined range of values for said change signal representing normal breathing of said person;   (g) monitoring said change signal which represents variations indicative of the amplitude of respiratory movement of said person;   (h) comparing the value of the monitored change signal with said predetermined range of values: and   (i) sounding an alarm when said change signal lies outside said predetermined range for a selected interval of time.